#include <stdio.h>

int main()
{
    int i = 0;
    float sum = 0;
    for(i = 1 ; i < 101 ; i++)
    {
        if(i%2 == 1)
        {
            sum = sum+1.0/i; 
        }
        else
        {
            sum = sum-1.0/i;
        }
    }
    printf("%f", sum);
    return 0; 
}